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CLEP Biology Practice Exam

Category - Biology

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Dutch elm disease is a fungal infection of elm trees that usually results in death.The disease has killed millions of NorthAmerican elm trees that were not resistant to the fungus. Scientists have bred resistant elms by crossing North American species with Asian species that show resistance.Which of the following best describes how natural selection would promote resistant elm populations once the resistance genes from the Asian species were successfully introduced?
  1. After encountering elms with resistance genes, fungi would
    avoid elms and begin to attack other tree species.
  2. Resistance would spread to all of the mature elms in a population from the few trees that acquired the resistance genes.
  3. By reproducing with each other, elm trees with resistance genes would create super-resistant elms with twice the number of resistance genes.
  4. Elm trees with resistance genes would survive and pass on resistance to offspring, while trees without resistance would more likely be killed by the fungus.
Explanation
Answer: D - Elm trees with resistance genes would survive and pass on resistance to offspring, while trees without resistance would more likely be killed by the fungus.
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